1. Field of the Invention
The present invention relates to a gas turbine engine, and especially to a seal arrangement formed on platforms of the rotary blades and the stationary vanes.
2. Description of the Related Art Including Information Disclosed Under 37 CFR 1.97 and 1.98
Rim seals are axial extensions of a turbine rotor blade, i.e., a bucket, which form a seal by overlapping with vane (nozzle) seal lands forming part of the fixed component of a gas turbine. The rim seal inhibits ingestion of hot gas from the flow path into gas turbine wheel spaces. Typically, rim seals are cast integrally as part of the blade or bucket, or are multiple overlays having multiple angel wings. Conventional airfoil platform seals have such a shape that the vane cannot be removed from the turbine without also removing the rotor blade because of the overlapping of adjacent platforms, i.e. the platform extending from the vane overlaps with the platform extending from the blade. Multiple overlap rim seals are assembled axially, and therefore the vanes cannot be removed radially from the casing due to interference with platforms on the blades that form the rim seal. U.S. Pat. No. 5,236,302 issued to Weisgerber et al on Aug. 17, 1993 shows a turbine disc interstage seal system in which an air seal is formed between adjacent platforms of the blade and the vane, where a finger of the vane platform extends in-between a space formed between two fingers extending from the blade platform. The vane in the Weisgerber invention cannot be removed from the turbine without removing the blade, since the fingers on the platforms interfere with each other.
Gas turbine engines also produce circumferential static pressure variations downstream from the airfoils. In a typical gas turbine, the gas stream flows past the airfoils both rotating and stationary, and the static pressure exiting the airfoil passage varies between two extreme pressures. This variation in static pressure acts across the rim seal at the platforms, and will cause undesirable hot gas ingestion into the wheel space without the presence of a rim seal. Multiple overlaps create a desirable buffer cavity or volume to dissipate this circumferential pressure variation.
It is an object of the present invention to provide for a platform design that will provide an airflow seal between adjacent blade and vane platforms and also allow for the vane to be removed from the turbine without removing the blade.
It is a further object of the present invention to provide for a platform seal that will attenuate the flow path asymmetry in the gas stream, or in other words to reduce the leakage across the platform seal due to the static pressure vibration acting on the platform seal.
It is a further object of the present invention to allow for removal of a vane in a radial direction instead of the axial direction, the vane having a platform seal arrangement with at least two overlaps forming the seal.